1. Field of the Invention
The present invention relates to a shooting pot shot size control feature incorporated within a cavity plate adjacent to a coinjection hot runner assembly in an injection molding machine, and in particular to an apparatus and method where a transverse-acting adjustable mechanical stop means is used to control the shot size of one of the shooting pots. Preferably, the shot size control is provided by a hydraulically actuated wedge structure that also allows the shooting pot to be charged while the mold is open.
2. Description of Related Art
Coinjection molding is typically used to mold multi-layered plastic packaging articles having a laminated wall structure. Each layer is typically passed through a different annular or circular passageway in a single nozzle structure and each layer is partially, sequentially, injected through the same gate. Some coinjection hot runner systems include shooting pots to meter material of one plastic resin so that each cavity of a multi-cavity mold receives an accurate dose of that resin in the molding cycle. Some design configurations use check valves to prevent backflow of the resin when the shooting pot discharges the resin through the nozzle.
U.S. Pat. No. 2,770,011 to Kelly teaches a hot runner valve gated mold in which the valve stems are opened and closed by an hydraulically actuated wedge shaped mechanism.
U.S. Pat. No. 4,095,931 to Reitan teaches a hot runner valve gated mold in which spool like shaft is moved axially to provide a camming action to cause the closing of the valve stems. Plastic pressure causes the valves stems to open at the appropriate time in the molding cycle.
U.S. Pat. No. 4,717,324 to Schad teaches a coinjection hot runner system including shooting pots that are activated hydraulically. The pistons are all oriented in the same direction so that the hydraulic actuation can be housed in the machine's stationary platen, or as taught in U.S. Pat. No. 6,152,721 to Schad, behind the stationary platen alongside the injection units.
In the configuration of the present invention, some of the shooting pot pistons are oriented toward the mold's parting line, and consequently their control becomes more problematic and cannot be accomplished by the configurations taught in the above art. Thus, what is needed is a shooting pot shot size control feature that allows for better shot control even when the parting line is open, permits more precise shot size metering, accommodates melt decompression, and allows for pullback prior to filling the shooting pots.